In these years, application of a nonnatural amino acid and a compound including a nonnatural amino acid to medicaments or agrochemicals has been progressed. It has been in a large numbers reported that especially, a nonnatural amino acid which has an aromatic group or a heterocyclic group in a terminal side chain thereof exhibits biologically interested activities and application to new medicaments or agrochemicals has been expected. Some processes of the preparation of nonnatural amino acids which have an aromatic group or a heterocyclic group in a terminal side chain thereof have been reported. However, as a process for the preparation utilizing C—C bond-formation reaction (coupling reaction) at a side chain in the amino acid, there are known the processes utilizing an organic metal regent such as cupper or palladium (See, for example nonpatent documents 1˜3.). However, there are following troubles: the organic metal reagent is generally expensive, the handling is troublesome, and purification procedure of the amino acid is difficult. Therefore, the development of an industrially effective process for the preparation thereof has been desired.
On the other hand, a process for the preparation of a nonnatural amino acid by coupling diethyl malonate to a side chain of an amino acid is reported (See, for example nonpatent documents 4˜6.). However, the examples of utility of a nonnatural amino acid which has malonic acid as a side chain, which have been reported are within the scope considered from malonic acid synthesis, namely remain only in elimination of one carbon dioxide molecule from malonic acid moiety. The method therefore, could not be applied to a process for the preparation of a nonnatural amino acid which has an aromatic group or a heterocyclic group in a terminal side chain thereof which needs elimination of two carbon dioxide molecules from the malonic acid moiety.    Nonpatent document 1: El Marini, A. et al., Bull. Soc. Chim. Fr., 554-558 (1989)    Nonpatent document 2: Jackson, R. F. W. et al., J. Org. Chem., 57, 3397-3404 (1992)    Nonpatent document 3: Collier, F. N. et al., Tetrahedron Lett., 41, 7115-7119 (2000)    Nonpatent document 4: Boggs, N. T. et al., J. Org. Chem., 44, 2262-2269 (1979)    Nonpatent document 5: Chauvel, E. N. et al., J. Med. Chem., 37, 2950-2957 (1994)    Nonpatent document 6: Ciapetti, P. et al., Tetrahedron Lett., 39, 3843-3846(1998)